STRUCTURE AND FUNCTION OF ESCHERICHIA-COLI MET REPRESSOR - SIMILARITIES AND CONTRASTS WITH TRP REPRESSOR

Transcription of genes encoding enzymes for the biosynthesis of methio nine and trytophan in Escherichia coli is regulated by the ligand-acti vated met and trp repressors. X-ray crystallographic studies show how these two small proteins, although similar in size and function, have totally different three-dimensional structures and specifically recogn ize their respective DNA operator sequences in different ways. A commo n feature is that both repressors bind as cooperative arrays to tandem repeats of 8 base-pair 'Met' or 'Trp boxes' respectively, and the con sensus sequences share the rare tetranucleotide CTAG. A series of stru ctural and functional studies have shown how the two repressors discri minate between their operators, using a combination of direct contacts between side chains and bases, and indirect sensing of conformational properties of the DNA.